Simple Indicators for Assessing Sustainability of Marine Aquaculture in Miyagi, Mie, and Kagoshima Prefectures, Japan

The assessment of aquaculture sustainability is a vital process that focuses on optimizing aquaculture production while mitigating environmental impacts, notably eutrophication. In this study, straightforward indicators were employed to assess the sustainability of coho salmon, red seabream, yellowtail, and bluefin tuna aquaculture in both enclosed bays and open water areas of Miyagi, Mie, and Kagoshima prefectures. This assessment was based on annual aquaculture production estimates, nutrient load, and farms' locations. The sustainability indicators, ΣI2 and ΣI3, exhibited significant variations among marine aquaculture setups in different enclosed bays. These indicators were further validated through the occurrences of red tides and the extent of bay closure. Higher values of sustainability indicators (ΣI2 and ΣI3) in enclosed bays correlated with more substantial aquatic environmental consequences, indicating lower marine aquaculture sustainability. The study highlighted a direct relationship between nutrient load and the distance of aquaculture farms from the bay mouth, showcasing the higher impacts of marine aquaculture on the aquatic environment in closer proximity. Bluefin tuna farming, known for its high feed conversion ratio and significant environmental impact, exhibited a higher nutrient load per unit production weight compared to other fish species. Coho salmon demonstrated a lower nutrient load per production, while red seabream and yellowtail exhibited relatively similar values. Interestingly, bluefin tuna's nutrient load per economic yield was relatively low due to the fish's high market price. These research findings provide valuable insights for aquaculture administrators, enabling them to estimate annual fish production and associated nutrient loads in marine aquaculture. This information is crucial for implementing an ecosystem approach, ensuring the long-term sustainability of marine aquaculture practices.